Even though membrane filtration is a promising technology, its large-scale industrial applicability is limited partly due to poor intrinsic membrane properties, but largely because of fouling of the membranes. The use of chemical biocides such as chlorine to control biofouling of membranes is widespread. However, most of these chemical biocides are not very effective at higher pH values and they react with dissolved chemicals to produce harmful by-products. Physical means to clean membranes like pigging, brushing, swabbing and jetting have been reported, but only work best as secondary methods to other biofilm removal methods. The use of bacteriophages, electrical current and nutrient control have also been explored, but these methods are either host specific or can take a long time to work and are not very cost effective.
The focus is now moving to modification of membrane surfaces in order to control fouling. Various metal elements in different oxidation states such as silver, copper, zinc, nickel, manganese, iron and lithium have been reported to possess antimicrobial properties. Some of these metals have been blended with polymers and made into fibers for use in filter media, wound dressing and other applications.
Quorum sensing (QS) is a process by which bacteria communicate, and forms an essential part of biofilm formation. Over the past few years, many publications and large amounts of data have become available on bacterial QS and interest among researchers in modulating QS using different approaches has increased. QS is not necessary for bacterial survival but helps in coordinating the community-based bacterial behavior. Therefore, the inhibition of QS only interrupts the desired phenotype. Biofilms are highly resistant to antibiotics and disinfection treatments and this results in persistent human infections and detrimental corrosion and equipment failure in industrial settings. Modification of surfaces and new inhibitor designs have been investigated for the control of biofilm formation in industrial settings.
Biofilm formation in filtration membranes is one of the major limitations associated with membrane technology. This reduces the quality and quantity of water in water purification systems and consequently results in higher treatment costs. Interference with QS may not bring about a universally beneficial effect, but makes the bacteria more susceptible to control or destruction by traditional means.
Furanone moieties have been found to have various medicinal properties, such as anticancer, cardiotonic, analgesic, antimicrobial, antiviral, antifungal, and anti-inflammatory properties. The use of furanone derivatives that inhibit QS in microorganisms is not a new phenomenon. Biochemical studies to understand different pathways of QS have been carried out. Furanone derivatives have been isolated from nature and have also been synthesized. Specific QS routes for these furanone derivatives have been reported. Research on clinical applications of furanone compounds is widespread. In a recent article, inhibition of QS by the furanone moiety was reported to have prevented soft rot caused by Pseudomonas aeruginosa from attacking onion plants. Hume et al. have coupled a furanone to polystyrene and used melt moulding to make disks having from 5 to 8% furanone on their surfaces which have up to 89% reduction of S. epidermidis biofilm formation. They also coated catheters with their polymer for in vivo tests which showed that furanone may have been worn or leached off in between 65 and 85 days.
This shows the potential and wide applicability of furanone-mediated QS inhibition. Furanones are analogs of homoserine lactones that appear to interfere with the development of typical biofilm structure, leaving these organisms more susceptible to treatment with biocides. Targeting QS is also advantageous compared to the use of antibiotics since there is no risk of the bacteria developing resistance, which causes serious control problems. Many natural products contain the core 3(2H)-furanone structure classified as a lactone. Because of the high synthetic and biological importance of furanone compounds, their chemistry has received considerable attention over the past two decades.